1. Field of the Invention
The present invention relates to a radio-type transmitting device which exchanges information with an external transmitting/receiving apparatus without any contact using a radio wave of a radio frequency band, a container including the above radio-type transmitting device, a transmitting/receiving system and a transmitting/receiving method including the above radio-type transmitting device. More specifically, it relates to a radio-type transmitting device, a container, a transmitting/receiving system and a transmitting/receiving method which can manage an amount of contents in the container.
2. Description of the Related Art
Recently, an apparatus which can manage products individually without any contact is being practically used in various fields by having a constitution that each of the products has a tag incorporating an IC chip in which individual information of the product is recorded in an EEPROM. For example, a RFID (Radio Frequency Identification) tag which transmits data and a power without any contact using a radio wave of a radio frequency band in writing/reading information in the EEPROM and supplying a power to the IC chip has come into practical use. In addition, the RFID tag is called a radio tag also and used in various kinds of frequency bands.
As shown in FIG. 19, a RFID tag 10 comprises a transmitting/receiving antenna 12 and the above IC chip 20 on a base member 11. A small RFID tag is a few millimeters in size and 1 gram or less in weight, for example. As shown in FIG. 20, the IC chip 20 comprises a power supply voltage generating unit 21 and a data processing unit 22 when it is functionally divided. The power supply voltage generating unit 21 generates an internal power supply voltage to be used in the data processing unit 22 on the basis of a radio wave of a radio frequency band which is transmitted from an external transmitting/receiving apparatus and received by the antenna 12, and comprises a rectification circuit 23 and a voltage moderation circuit 24 generating a constant voltage. The data processing unit 22 comprises a receive circuit 25 which is connected to the antenna 12 and receives information transmitted from the external transmitting/receiving apparatus, a controller 26 which has a microcomputer for processing the received information to control the RFID tag 10, an information storage unit 27 including an EEPROM for storing individual information as described above, and a send circuit 28 which transmits processed information by the controller 26 to the external transmitting/receiving apparatus through the antenna 12.
It is known in general that propagation of a radio wave in free space is proportional to a transmit power and a receiving sensitivity and inversely proportional to the square of a distance between communications. Therefore, the RFID tag is mounted on a surface of an object to be measured or arranged in the vicinity of the external transmitting/receiving apparatus in order to facilitate the communication. In addition, although there are a transmission method using electromagnetic induction and a transmission method using a microwave in the RFID tag depending on the radio frequency band to be used, the communication distance is determined by a radio power emitted from the external transmitting/receiving apparatus and a radio power emitted from the RFID tag in either case. For example, in a band of 13.56 MHz, a signal and a power are exchanged between loop antennas by electromagnetic induction using coil-shaped loop antennas.
As another communication scheme, load modulation scheme is known. In this scheme, by switching of internal circuits in a RFID tag, the tag makes a load of antenna sent out from an external transmitting/receiving apparatus change instead of the above way sending the radio power from the RFID tag. The load modulation scheme can also obtain effects similar to that of the way sending the radio power.
As the communication distance becomes long, a transmission amount of the power becomes small and the communication cannot be implemented, so a power supply voltage in the RFID tag is lowered. In this case, since information writing error to an internal memory such as the EEPROM might be generated, there is a mechanism in the tag, in which the communication is cut so as to avoid a malfunction when the receive power becomes a predetermined value or less. Meanwhile, when the communication distance is too short, since the transmit power is too high, an excessive voltage is generated in the RFID tag and a defect might be generated. Thus, a circuit restricting the generation of the power supply voltage is also provided in the RFID tag. In general, when a radio wave of a frequency of 13.56 MHz is used, the communication distance is limited in a range from a few centimeters to several tens centimeters depending on specifications of the IC chip and the antenna.
In addition, when a liquid product filled in a container is sold, it is necessary to manage not only characteristic data of the liquid product but also an amount of the contents in many cases. In addition, it is important to manage a remaining amount of the contents while the product is used.
For example, according to a DMFC (Direct Methanol Fuel Cell) in which a power is generated using methanol as a direct fuel, since there are fuel containers containing methanol fuels having various concentrations, in order to appropriately generate a power to provide a maximum output in the fuel cell, it is necessary to supply methanol having an appropriate concentration, that is, about 1 mol %, for example. Thus, for a fuel cell system in which high-concentration methanol solution is supplied and diluted to generate the power, an initial methanol concentration is important information. In this case, when the RFID tag is used, the methanol concentration can be written in its internal memory and the concentration can be easily managed.
In addition, although a power generating operation can be continued semipermanently as long as the fuel is supplied in the fuel cell, the power generation is stopped naturally when the fuel runs out. Therefore, in the fuel cell system, the management of the remaining amount of the fuel is very important. In general, as a method of managing the contents, there is a method of measuring a liquid level using a sensor to estimate the liquid level based on a conductivity or a dielectric constant of the solution, a liquid surface level sensor using reflection of supersonic wave, or the like. However, according to the above method, its cost is high and the number of circuit components for detecting the liquid level is increased, so that the device becomes large and there is a problem in practical use. Therefore, when the fuel cell is used as a power supply for a portable electronic device such as a laptop personal computer, the above sensor cannot be used as a remaining amount detection device of the methanol fuel in the fuel cell.
The above conventional art is disclosed in, for example, Japanese Unexamined Patent Publication No. 9-130999 and Japanese Unexamined Patent Publication No. 6-325229.
As described above, the RFID tag can be appropriately used to manage contents and since the RFID tag itself can be formed in very small size and light in weight, it can be effectively used in a portable electronic device which needs to be small and light.
However, according to the conventional technique using the RFID tag, the RFID tag is arranged within the predetermined transmittable distance so that information is exchanged between the external transmitting/receiving apparatus and the RFID tag as described above. Namely, the external transmitting/receiving apparatus transmits the radio wave with a constant output which corresponds to a communication distance ensuring the predetermined communication distance. Furthermore, according to the conventional technique, only exchanging information to the internal memory is performed between the external transmitting/receiving apparatus and the RFID tag, that is, only information in the internal memory such as the EEPROM and information of a result after the information of the internal memory is processed are communicated.
In other words, according to the conventional technique using the RFID tag, the communication cannot be implemented when the RFID tag exists beyond a set communication range and goes missing. Thus, when the existing position of the RFID tag is unknown, it is out of consideration. Therefore, there has been no proposal to make the external transmitting/receiving apparatus detect the missing RFID tag.
The above Japanese Unexamined Patent Publication No. 6-325229 discloses the communication scheme being able to measure a distance by modulating intervals of response data with reference to a direct voltage obtained by rectifying received radio waves. However in this scheme, since it is necessary to make an interval between response signals even if a lot of intermittent data are sent, communications need waste times. Thus there is a problem that communication efficiency is bad and quick response can not be done.